The present invention relates to combiner assemblies having a combiner through which a user views an outside scene overlaid with a projected image. Such combiner assemblies can be used in head up displays.
FIG. 1 illustrates a typical combiner assembly 10 used in a head up display, which comprises an optical combiner 11 mounted to a housing 12 which is arranged for mounting to a roof structure 13 of a flight deck of an aircraft. The combiner assembly 10 comprises a semi-reflective surface and is arranged to present flight, navigation, guidance and other information to a user who views an outside scene through the optical combiner 11. This is accomplished by projecting images from a display forming section 14, typically comprising a cathode ray tube, onto the semi-reflective surface which is arranged to allow the user to view the outside scene through the optical combiner 11 and to reflect the images from the display forming section 14 along a sight line of the user. The image conveyed to the user is collimated and conformal such that the user views the outside scene overlaid with the projected images. Typically, the optical combiner 11 is pivotally mounted, not illustrated, to the housing 12 such that the optical combiner 11 can be moved from a stowed position above the user's head to a deployed position in front of the user and coincident with the user's sight line.
However, if the optical combiner 11 is not properly secured in the stowed position it may rotate from its position such that it interferes with the user's vision, or worse, impacts the user's head. Furthermore, should the user move forward while the optical combiner 11 is in the deployed position, perhaps due to the aircraft flying into turbulent air, and impacts the optical combiner 11 then this could interfere with the safe and proper handling of the aircraft.